The invention is based on a fuel injection system for internal combustion engine. In one such fuel injection system, known from German Patent Application DE-A 44 06 901, the electromagnetically driven 3/2-way control valve that electromagnetically controls the pressure in the control chamber is designed such that in one position, the control valve connects the valve chamber with the high-pressure fuel source, which then also communicates with the control chamber at the same time, and in another position connects the valve chamber and at the same time the control chamber with the relief chamber. A throttle is formed downstream of the valve seat in the control valve in the outflow conduit through which the relief speed and consequently the opening rate of the fuel injection valve member can be reduced at the injection onset. On the inlet side to the control chamber, conversely, no flow limitation is provided, so that the end of the fuel injection event can be effected rapidly by means of a rapid pressure buildup in the control chamber that puts the fuel injection valve member into the closing position. This arrangement has the disadvantage that the outflowing fuel, by the diversion process of which the fuel injection onset is intended to be initiated, is throttled downstream of the valve seat, which leads to a pressure buildup upstream of the throttle. If the diversion occurs suddenly, the result is feedback forces on the control valve member, which adversely affect the switching times of the control valve because they counteract the controlling motion of the valve member. The final outcome is that injection quantities in successive injection events vary considerably.
With the fuel injection system according to the invention hydraulic surges that occur as pressure fluid and is diverted from the control chamber to the control valve member have hardly any effect on the uniformity of the injection events. Disruptive feedback is averted by the throttle located upstream of the valve seat. It is advantageous that the throttle is realized on the valve body without requiring any additional component or additional machining steps. In an advantageous refinement, an additional damping of the hydraulic surges on the valve body is effected. The collar has the effect that the quantity of pressure fluid flowing into the valve chamber, which quantity is meant to be delivered for control purposes to the control chamber, is throttled downstream of the valve seat and by a pressure buildup, an additional force on the valve body in the opening direction thereof is created. Thus, the pressure required to terminate the injection can be built up more rapidly in the control chamber. The result is accordingly faster switching times of the control valve. When the second valve seat opens, in the process of which the valve body moves in the closing direction to the first valve seat, a delay upon closure of the valve seat occurs because of the presence of the collar, and thus a delay in the relief of the control chamber and a corresponding desired delay, already sought by the throttle, in the pressure rise at the injection valve member.